Biochemical studies of the last several years have shown that uptake of inorganic iron and its transport in microorganisms takes place using very powerful chelating agents which coordinate to iron via hydroxamate, catechol or other functional groups. The siderochromes are a class of compounds which are used by various microorganisms to extract ferric ion from their solution environment and concentrate it within the cells. Transport of the siderochromes across cell membranes is very conformation dependent; the metal complexes are rapidly passed into the cell while the demetallo forms often are not. Several isomers of metal complexes in which the ferric ion has been replaced by the kinetically inert chromic ion have been isolated and the transport properties of one such isomer has been studied. We propose to continue the preparation of coordination isomers of the siderochromes and simple model compounds. Determination of structure will be primarily by means of circular dichroism but also will include single crystal X-ray diffraction. Finally, transport studies of several of the isomers will be undertaken in microbial systems.